Field
Embodiments of the disclosure relate generally to supersonic inlets for aircraft jet engines and more particularly to a caret inlet having variable geometry for off-design flight conditions.
Background
Engine inlets for supersonic aircraft have complex aerodynamic requirements based on Mach number and other flight conditions. Fixed inlet geometries typically have highest efficiency at one specific Mach number and flight condition. Operation at other speeds or flight conditions results in degradation of the aerodynamic performance or efficiency of the inlet. To allow flight at varying Mach number, mechanical systems to adjust the capture area and ramp geometry of the inlet may be employed to increase efficiency. An existing solution to a variable ramps and variable capture inlet is the F-15 Eagle produced by The Boeing Company. This inlet system is highly efficient and is recognized as an optimized inlet design. However, later-generation fighters require unique shaping where the inlet aperture edges are highly swept. In such aircraft a caret-type inlet system is employed. Examples of aircraft employing such inlets are the F-18E/F Super Hornet produced by The Boeing Company and the F-22 Raptor produced by Lockheed Martin. These inlets are fixed geometry inlets and were designed for optimized operation at a particular flight Mach number. At off-design Mach numbers in a fixed-geometry inlet system the shockwave may detach from the ramp leading edge of the caret because the inlet is no longer on-design. In addition, the flow field inside the inlet aperture is 3-dimensional and the shock wave is 3-dimensional as well. The combination of these can decrease inlet total pressure recovery and increase inlet distortion.
It is therefore desirable to provide an inlet which will help improve inlet performance at off-design Mach numbers by maintaining an attached 2-D shock wave and 2-D flow field inside the inlet aperture.